Composition of piper nigrum L. essential oils extracted by classical hydrodistillation and microwave-assisted hydrodistillation and inhibitory effect on the corrosion of mild steel in hydrochloric acid

The inhibition of the corrosion of mild steel in 1 m hcl by the seeds essential oil of piper nigrum; extracted through microwave-assisted hydrodistillation (mhd) and conventional hydrodistillation (chd) method; has been studied using weight loss,potentiodynamic polarization method and electrochemical impedance spectroscopy measurements at different concentrations and effect of temperature. three amounts of essential oils obtained by classical hydrodistillation and by microwave hydrodistillation on low and high microwave power are tested on the corrosion inhibition of mild steel. the measurements show that inhibition efficiencies increase with the increasing concentration of the inhibitor. the results of weight loss studies correlated well with those of impedance and polarization studies. the maximum inhibition efficiency (95.99%) was found at 0.6g/l at 308 k,after 6 h as immersion time. this reveals that inhibitive action of the inhibitor was mainly due to adsorption on the mild steel surface and blocking of the active sites. the above results showed that inhibitor acted as a mixed-type corrosion inhibitor. the adsorption of has on the mild steel surface obeyed the langmuir adsorption isotherm. this was supported by the impedance measurements which showed a change in the charge transfer resistance and double layer capacitance,indicating the adsorption of has on the mild steel surface.